1. Field of the Invention
The present invention relates to a laminated core structure of a motor.
2. Description of Related Art
When a laminated core structure of a motor is formed, as a method for laminating and fastening thin iron sheets, which have been obtained by blanking a silicon steel sheet etc., a method called caulking has generally been used in which uneven parts are formed in a part of the iron sheet by a fabrication method called embossing, and the uneven parts are engaged with each other.
In the fastening caused by caulking, the uneven part exerts resistance to the passage of magnetic flux, so that the magnetic balance of the whole of a magnetic circuit is upset, and the motor characteristics are influenced adversely. Therefore, proposals for solving this problem have been made.
FIGS. 6 and 7 show a conventional laminated core structure of a stepping motor. FIG. 6 shows a stator iron sheet 100 used for a stator iron core of the stepping motor, and FIG. 7 shows a rotor iron sheet 105 used for a rotor iron core thereof (refer to Japanese Unexamined Patent Application Publication No. 2001-292541 that discloses a related art).
For this stator iron sheet 100, an electrical steel sheet is used as the material thereof. The stator iron sheet 100 is provided with a plurality of (eight in the example shown in the figure) magnetic poles 101 arranged at fixed intervals along the circumferential direction on the inner peripheral side of a substantially square-shaped sheet so as to project toward the center direction. In the root part of the magnetic pole 101, a bridge part 101a around which a stator winding is wound is provided, and between the magnetic poles 101, a slot 101b for allowing the stator winding to pass through is provided. At four corners of the stator iron sheet 100, assembling screw holes 102 are provided, and in portions on both sides of the assembling screw hole 102, caulking uneven parts 103 are provided. Also, the bridge part 101a of the magnetic pole 101 is also provided with a caulking uneven part 104.
The rotor iron sheet 105 is provided with a plurality of caulking uneven parts 106 arranged at fixed intervals along the circumferential direction in the peripheral edge portion of a disc-shaped sheet.
According to this related art, the stator iron sheets 100 are assembled integrally by lapping and laminating the stator iron sheets 100 on each other so that the caulking uneven parts 103 and the caulking uneven parts 104 each are aligned with each other, and pushing the caulking uneven parts 103 and the caulking uneven parts in each other, by which the stator iron core is manufactured. The rotor iron sheets 105 are also assembled integrally by lapping and laminating the caulking uneven parts 106 and by pushing the caulking uneven parts 106 in each other, by which the rotor iron core is manufactured.
The caulking uneven part 103 of this related art has a diameter of 1 mm or smaller, and the caulking uneven part 104 has a diameter of 0.8 mm or smaller. Also, the caulking uneven part 106 of the rotor iron sheet 105 has a diameter of 0.8 mm or smaller.
The height of a convex part of the caulking uneven part 103 is set so as to be about 70% of the sheet thickness.
In Japanese Unexamined Patent Application Publication No. 2001-292541, the center shift between a die and a punch for embossing is set at 3 μm or smaller. Thereby, when the stator iron sheets 100 and the rotor iron sheets 105 are laminated by engaging the caulking uneven parts 103, 104 and 106 with each other, the occurrence of galling in the uneven part engagement portions is eliminated, and thereby thin steel sheets can be brought into close contact with each other.
A low-loss laminated core obtained by figuring out the shape and size of the caulking part has been proposed.
As shown in FIG. 8, a magnetic path X of a hybrid stepping motor is usually formed as indicated by the arrow marks. Therefore, in the technique in Japanese Unexamined Patent Application Publication No. 2001-292541 as well, the caulking uneven parts are formed in intermediate portions in the magnetic path X, so that the caulking uneven parts still exist as magnetic resistance, which causes a core loss.
Also, the rotor of the hybrid stepping motor is generally constructed so that the rotor is formed by holding a permanent magnet using a magnet of rare earth etc. between two rotor iron cores. Therefore, in the hybrid stepping motor, the quantity of iron material for the rotor iron core is considerably smaller than that for the stator iron core.
For this reason, a loss of motor (core loss) produced by the decrease in magnetic characteristics caused by the caulking of rotor iron core has been thought to be considerably small. Therefore, the caulking position of rotor iron core has so far not been studied sufficiently.